Nowadays, power tools, especially wobble-driven reciprocating saws, are easier to be operated, and their dimensions become more compact. In a reciprocating saw, a counterweight as a balance mechanism is used to minimize vibration of the reciprocating saw during operation, thereby protecting users from the risk of fatigue or being cut when using the reciprocating saw.
In GB 2256905A, a portable power-driven electrical reciprocating saw is disclosed, which comprises a dual wobble plate including a front wobble plate and a back wobble plate, a wobble arm of the front wobble plate driving a spindle to reciprocate, while a wobble arm of the back wobble plate driving a counterweight to reciprocate with a 180° phase deviation relative to the spindle, so as to realize counterbalance function of the reciprocating saw during operation. Although the counterweight of this reciprocating saw is coaxial with the spindle to gain proper counterbalance effect and reduce vibration, the overall dimension of the reciprocating saw is very large due to the dual wobble plate, so it is not suitable for the reciprocating saw to be used as a compact reciprocating saw.
In U.S. Pat. No. 7,707,729B2, another type of reciprocating saw is disclosed, which improves the structure of a wobble arm of a back wobble plate to further reduce vibration of the reciprocating saw. However, the structure of this reciprocating saw is very complicated, making it difficult for the reciprocating saw to be manufactured and maintained.
In DE 19648972B4, yet another type of reciprocating saw is disclosed. FIGS. 1 and 2 show a longitudinal section view and a cross section view of the reciprocating saw respectively. As shown in FIGS. 1 and 2, in this reciprocating saw, a rotating movement is transmitted from a small-diameter gear 1 to a sub-shaft 3 via a large-diameter gear 2, a single wobble plate 4 is then driven to reciprocate by the sub-shaft 3, the single wobble plate 4 having a front arm 5 and a back arm 6 at its opposite ends. A spindle 9 is driven to reciprocate by the front arm 5 while a counterweight 8 guided by two guiding rods 11 is driven to reciprocate by the back rum 6 via a hole 7. The structure of this reciprocating saw is simple and compact. However, due to a long distance between the gravity center 10 of the counterweight 8 and the hole 7, as shown in FIG. 2, an additional torque load is created therebetween. Further, due to a long distance between the gravity center 10 of the counterweight 8 and the guiding rods 11, an additional torque load is created therebetween as well. These torque loads cause the counterweight 8, the hole 7 and the guiding rods 11 to be worn faster, thereby shortening their service life. In addition, due to a long distance between the gravity center 10 of the counterweight 8 and the gravity center of the spindle 9, a heavy torque load is created between the counterweight 8 and the spindle 9, thereby increasing vibration of the reciprocating saw.